When taking a shit, having someone sit on your lap aiming their anus between the first person's legs. Both people shit at the same time, creating a "double" effect and saving water in the process. For utmost efficiency, time the splashes similar to Olympic synchronized diving.

She sat on my lap while I was on the toilet so we could double decker that shit.

One Bro Gets a blowjob while the girl is on all fours on the ground. While this is happening, another Bro gives it to the girl from behind. Both Bro's preceed to run forwards until the girl is bent in half. Then she makes both Bro's a sandwich.

-"dude she's in the hospital!"

-"Yea i know, after we double-deckered her, she made us sandwichs, then we told her to walk to the hospital."